We propose to acquire a state-of-the-art hybrid mass spectrometer (i.e., a Thermo-Electron Orbitrap or equivalent) for core and collaborative research and to provide service to the biomedical research community at Washington University (WU) and nationwide. Interfaced to the mass spectrometer will be a nano-HPLC. An autosampler and nanospray ionization source will be provided by the host laboratory to complete the installation. The integrated system will provide a platform for the separation and analysis of biomolecules, especially peptides as antigens or from post-translationally modified proteins. One specific aim of this acquisition is to further the NIH-funded research of eight major users: (1) Finding diabetogenic peptides presented by MHCs (Dr. Emil R. Unanue, WU), (2) Locating steroid binding sites on GABA receptors for anesthesia and pain management (Dr. Alex Evers, WU), (3) Mapping out the expression of the mitochondrial proteins in HIV patients at various stages of the disease and during different treatment regimens (Dr. Kevin Yarasheski, WU), (4) Finding the role of posttranslational modifications of histones in nucleolar dominance and gene silencing (Dr. Craig Pikaard, WU), (5) Studying DNA damage and repair mechanisms involved in UV-induced photodamage to DNA (Dr. John-Stephen Taylor, WU), (6) Determining protein structure and interactions using H/D exchange and fast hydroxyl radical reactions (Dr. Michael Gross, WU), (7) Studying the structure and metal-binding properties of human centrin 2, an EF-hand calcium binding protein important in centrosome function, cell duplication, and nucleotide excision repair (Dr. Rajiv Kumar, Mayo Clinic), (8) Finding the mechanism of redox activity in Ape-1 endonuclease, a base excision repair enzyme expressed in several cancers (Dr. Millie Georgiadis, Indiana University). The second specific aim is to provide accurate mass and occasional proteomics mass spectrometry service, including method development, to minor and new users and in so doing, stimulate the development of new collaborative research. Five of the above NIH-funded projects arose from this kind of preliminary work. Relevance This instrument acquisition has direct impact on the public health by supporting forefront research on immunity and diabetes, anesthesia and pain management, cancer, and AIDS. In addition, it will have broad impact by providing nationwide mass spectrometry service for researchers whose MS requirements are sufficiently simple that they do not require collaborative efforts. [unreadable] [unreadable] [unreadable]